File Browser - missing an input box
The box you are looking for is the file name box, where you input the file name for the undergoing operation. Those buttons allow to increment or decrement the file numbering automatically

If you open the File Browser as a regular editor, there is no "default file action", it just open for view and navigation purposes, and as such the file name box is unavailable because there is no active operation to preform.

To have the name box available and the increment/decrement visible, the file manager has to be invoked from a menu to preform some IO action, rather than a permanently open browser part of the workspace layout.



If you go to File > Import or File > Save as or any other file operation like linking, appending, exporting, or any other operation that requires specifying a file the name box will show, along with the buttons.